1. Field of the Invention
The present invention relates to a light-transmittable linear photocatalytic filter material having a long and narrow light-transmittable linear material and a number of particulate materials provided on an outer surface of the linear material, and further having a photocatalytic layer formed on or above an outer surface of the linear material and the number of particulate materials; a filter formed of such light-transmittable linear photocatalytic filter materials; and a process for producing the above filter material.
2. Prior Art
A photocatalyst is a material that exhibits functions of sterilization, antimicrobial activity, decomposition, deodorization, non-soiling, non-fogging, and the like when exposed to light. When titanium dioxide, a typical example of the photocatalyst, is exposed to light, the titanium dioxide causes an intense redox reaction on its surface to decompose a substance that is in contact with the surface. For example, when the above substance is an organic substance, the organic substance is decomposed into carbon dioxide gas and water. The photocatalyst decomposes, for example, environmental pollutants such as microorganisms, virus, malodorous substances, dioxin, trichloroethylene, etc., and endocrine-disturbing chemicals that may cause a sick building syndrome.
Attempts are being made to utilize the above photocatalysis for a filter and apply the filter to disposing of various liquids, disposing of various gases and environmental cleaning.
For providing a high-performance photocatalytic filter at a less expensive price, there is proposed a photocatalytic filter material having a filter base material formed by bonding particulate materials to a surface of a long and narrow light-transmittable linear material to form projections and a photocatalyst layer formed on the filter base material (JP-A-10-71312).
When a large number of such photocatalytic filter materials are bundled with aligning their ends on each side to constitute a photocatalytic filter, gaps are formed among the filter materials adjacent side by side owing to the presence of the above projections, so that a fluid to be disposed of can be allowed to flow through the above gaps. Further, passage spaces forming the above gaps do not easily change with the passage of time or are stabilized, so that the photocatalytic filter can maintain performances as a filter for a long period of time.
In the above photocatalytic filter, one end surface or each end surface of a bundle formed of a number of photocatalytic filter materials is provided with a light incidence portion, and light such as ultraviolet ray is allowed to enter the light incidence portion and is propagated inside the photocatalytic filter materials. Since the photocatalyst layer (e.g., titanium dioxide) has a higher refractive index than the linear material (e.g., glass fiber), the propagated light above has no components that undergo total reflection, so that it leaks into the photocatalyst layer.
When an inorganic adhesive containing silica as a main component is used as an adhesive for bonding particulate materials as projections to outer side surfaces of the light-transmittable linear materials, the refractive index of the adhesive satisfies the condition of total reflection since it is equivalent to, or slightly lower than, the refractive index of the light-transmittable linear materials, so that no light leaks into the photocatalyst layer. Since, however, microscopic pores are formed in an interface between the light-transmittable linear materials and the adhesive after the adhesive is baked, there occurs light that leaks into the photocatalyst layer through the pores as base points. Therefore, the light that enters the light incidence portion is not propagated far but gradually leaks into the photocatalyst layer, and the photocatalyst layer is irradiated with the light that has leaked into it.
On the other hand, a fluid to be disposed of is allowed to flow xe2x80x9cuniformlyxe2x80x9d through the passage of gaps of a bundle of a number of the photocatalytic filter materials, whereby the photocatalytic filter traps contaminants contained in the fluid to be disposed of, with the surface of the photocatalyst layer. The photocatalyst layer is irradiated with the above light that leaks into it, whereby the trapped contaminants are decomposed by photocatalysis.
It is expected that the efficiency of the photocatalysis is increased with an increase in the number of photocatalytic filter materials bundled. In reality, however, when the number of the photocatalytic filter materials bundled comes to be thousands, tens of thousands or more, there is caused another new problems.
For example, as shown in FIG. 11, a number of quartz glass spheres 2 (average particle diameter; 50 xcexcm) as particulate materials are bonded to an outer surface of a fiber 1 made of glass as a long and narrow light-transmittable linear material with an adhesive. Further, a titanium dioxide layer 4 (thickness; 2 xcexcm) is formed on the above number of quartz glass spheres 2 and an outer surface of the fiber 1 made of quartz glass by a known dipping method, to prepare a glass fiber photocatalytic filter material 90. About 70,000 photocatalytic filter materials 90 are bundled to obtain a photocatalytic filter. In the thus-obtained photocatalytic filter, the following abnormal phenomenon takes place.
As shown in FIG. 12, when such photocatalytic filter materials 90 are bundled with their ends on each side aligned, and housed in a cylindrical case 5 made of aluminum (internal diameter; 70 mmxcfx86, a length; 200 mm) to constitute a photocatalytic filter 91, the photocatalytic filter 91 has the form of a barrel as shown in FIG. 12. The above xe2x80x9cform of a barrelxe2x80x9d means that photocatalytic filter materials 90 positioned on outer side surface of central portion of the photocatalytic filter 91 swell outwardly in a convex form. As shown in FIG. 12, the middle portions of the photocatalytic filter materials 90 are in close contact with the internal side surface of the cylindrical case 5, and a space portion 7 occurs near an opening on each side of the photocatalytic filter.
The photocatalytic filter 91 sufficiently performs as a filter only when a fluid to be disposed of is allowed to flow xe2x80x9cuniformlyxe2x80x9d through the passage of gaps formed by particulate materials 2 among the photocatalytic filter materials 90 of the photocatalytic filter 91 formed by bundling a number of the photocatalytic filter materials 90 with aligning their ends on each side. In the above space portion 7, however, the flow of the fluid abnormally increases in amount, and the flow comes to be non-uniform, so that the photocatalytic filter cannot sufficiently work as a filter.
As shown in FIG. 13, when an overflow state of a water stream 8 is observed in a test in which a photocatalytic filter formed of a number of photocatalytic filter materials 90 is allowed to stand upright and the water is allowed to flow upwardly in a stream 8 (flow rate: 2 liters/minute), water stream 8 above the above space portion 7 rapidly flows to cause a standing portion 6. The above test result shows the above abnormal phenomenon of a fluid caused by the space portion 7.
It is therefore an object of the present invention to provide light-transmittable linear photocatalytic filter materials that can be arranged in parallel in the longitudinal direction without causing a filter to have the form of a barrel when the filter is made of a bundle of a number of such photocatalytic filter materials; a filter made of the above photocatalytic filter materials, and a process for the production of the above photocatalytic filter materials.
According to a first aspect of the present invention for achieving the above object, there is provided a light-transmittable linear photocatalytic filter material comprising a light-transmittable linear material, a number of particulate materials bonded to an outer side surface of the light-transmittable linear material and a photocatalyst layer formed on said outer side surface and said number of particulate materials,
said light-transmittable linear photocatalytic filter material being for the production of a light-transmittable linear photocatalytic filter in which light enters one end or both ends of said light-transmittable linear material, propagates inside said light-transmittable linear material and leaks into said photocatalyst layer and said photocatalyst layer is irradiated with the leaked light, characterized in that:
a maximum value of heights from the outer side surface of the linear material to the surface of the photocatalyst layer in a central region of said light-transmittable linear material in the longitudinal direction is smaller than a maximum value of heights from the outer side surface of the linear material to the surface of the photocatalyst layer in regions of both ends thereof.
According to a second aspect of the present invention for achieving the above object, there is provided a light-transmittable linear photocatalytic filter material that is according to the first aspect of the present invention and also satisfies requirements that the central region of the outer surface of said light-transmittable linear material in the longitudinal direction has a length in the range of from 20% to 60% based on the total length of said outer surface; that each end region of the outer surface of said light-transmittable linear material in the longitudinal direction has a length in the range of from 20% to 40% based on said total length; and that said particulate materials distributed in said central region has a lower density than said particulate materials -distributed in each end region.
According to a third aspect of the present invention for achieving the above object, there is provided a light-transmittable linear photocatalytic filter comprising a bundle of a large number of light-transmittable linear photocatalytic filter materials according to the first or second aspect of the present invention.
According to a fourth aspect of the present invention for achieving the above object, there is provide a process for producing light-transmittable linear photocatalytic filter materials each of which is made of a long and narrow linear material, a number of particulate materials that are bonded to an outer side surface of the linear material in a predetermined distribution density, and a photocatalyst layer formed on said outer surface and said particulate materials, comprising the steps of:
mixing a number of light-transmittable linear materials, a number of particulate materials and a predetermined amount of an adhesive to temporarily bond said light-transmittable linear materials and said particulate materials,
housing said light-transmittable linear materials and said particulate materials that are temporarily bonded, in a container having a pair of facing net-shaped surfaces,
placing weights having a bottom having a predetermined area and having a predetermined loading weight on central portions of said net-shaped surfaces to press said light-transmittable linear materials and said particulate materials, and
rocking or vibrating said container in a state where said light-transmittable linear materials and said particulate materials are pressed, for a predetermined time period, to rub off particulate materials on a central region of said temporarily bonded linear materials in the longitudinal direction.